Electric amplifying system



Jan. 1', 1935. B. F. MIESSNER' 1 ,985,945

ELECTRIC AMPLIFYING SYSTEM Original Fil ed Ja 15, 1929 INVENTOR ATTORNEY- Patented Jan. 1, 1935 "by mesne "as'signmentgto Radi A er D l war 1 a.

This' invention relates to eleetric amplifying systems employing vacuum tubesasam'pIifiers o'r repeaters andhasforits prinoipalpbject to provide an improved system of this character 10 which is highly eflicient in operation and-:ex- 'ceiitionally economical in'the use of current employedior energizing the several-tube circuits; The sources of current customarily employed 'for energizing the plate" circuitsof the vacuum tubes are batteries-or alternating current rect'i- -fie'r's and'"filters. The cost;-;weightand-spa'ce oc- 'cupied -by a battery is' roug hly proportionalyto v fiediorn'i otmy inventioni its ampere h'our capacity; that is 'ofqtwo batteries'having the same length of life, one giving a higher current costs-more; weighsmore and occupies more space than onegiving a-lesscurrent? Also theco'st of rectifiers" and ifilt'ers' employed for plate circuit supply increases: with increased current capacity. The "systemconstructed inacoordance-with the'present invention is designed to reduce to .a minimum the currentsupplie'd to the tube plate circuits and'for this purpose instead of connecting-*allxthe plate circuits to' the 'source' of supplyin' parallel or derived 'c'ircuit relation as now customary, I connect the plate'circuits of twofor more'tubes to the source of supply in series with one an: other. Iain thereforeable to-use the B supply current a number 'oftimes as -it flows through 30 different tubes' in succession.

When my invention is appliedtoa system employing 'apower tubein thelastfstage, which tube-"consumes a greater plate current than any of there'maining tubes; '1 preierably divide the 35 plate returncircuit of the" power tube into a number of parallel circuits and use the currents in the parallel circuits for different purposes. Thus one or more of these" parallel circuits may form another plate circuitor other plate-circuits.

.140 Also I may if desired'use part of the power tube plate return asa filament or cathode heating circuit." I mayfurtliermore connect the grid of the power tube to some point-in the platereturn circuit so as to utilize the'potential drop between the cathode of the powertube and'such' point, for supplying the desired biasing potential to'jthe grid-of the-power tube,

The systems hereinafter particularly described disclose several featuresof advantage'oth'ei' than 5 those-above mentioned. Amongfsuch other fea 'tures' isthe provision of an improvedcoupling between different stages of the system; which coupling may be connectedwith the remainder of the system in different ways so'as to produce regeneration or degeneration asdesireda N wa k N Ya l 1 1 .iit utaitn itana 15,

- Renewed May 10,1933; 7

recla ms 5 M ".eFlgure l is adiagrammati view showing asim- -p1e1 embodiment 'of my inventiong consisting of '&two stage audio frequency amplifying system; F Figure 2 i is a circuit diagram showing an 'e'xt'e'nF- sionT of the system 3 shown inf-Figure 1; te -include I a 'det'ectorstage andone additional stage of I 'and 'pl'ate voltagesj and la'rge -plate cui rentb" I-provide atiaiisfcirnien 110 havingraj-Corporation oi 'icorporation of Additional features and ob ect's ofiny invention will: appear from the' following description *taken inconnection wlth the-accompanying'drawaudio I frequency ampliflcation iafr ic'l 3 Figure 31s a circuit'diagran'ihow ingafmodi- Referring to Figure" '1', T1 and T2 yrepresent three electrode vacuum tubes successive stages it of audio frequency amplification: Tube -T 1; is a power tub'e and: designed} for relativly high grid - nonme 'iurposetr 'energ-izingithe iibe-oircu s primary winding 511'; which may -convei liently b supplied with alternating current fiom -the' usu'al house lighting Y circuit. 4 :The transformer 1'0 has =fou r "secondary windings 13, i4;- is and' ie; respectively.

The winding 13 is connected to thefilainent of tube 4 and :su pnes c'u'rrent for he'ating the filament to it's operating -temp'erature.-" Winding 14 is connected to the filament of power tube T1 and supplies current forheating the filament of this tube:- Win'dings-IS and 16 supply current respectively to mam-meet andplate' circuitof supply f'or the plate circui-tsof" the tubes T1 and 01" the-filter is' connected tothe'plate 'of 'tubeTl through? the'f primary- 524* of transformer; the

secondaryi'lof :which is connected :to an output .circuitlmvhich may include .:.-a" translatingl device such as*a -loudi'spcakennot shown.

; Bridged across: the terminals, of the ffilament of the resistance 25 is;,a sliderdfi whichis grounded .through a resistance}?! .The. plate f tube Q'I Z 'isconnecte'd to the slide 26 through r h r a wanes 29. The/secondaryof'transiormer 31fis connected at on end j'to. the grid of tubi'ri Land. iatfithe which is' adjustable along the resistance 271"] A relatively highjcapaicity cjon'denser f $0 is connecttube-T1 is a resistance gfi andadjustable along I other fend through a' 're'sistanoe'. 32 tofa' lid'er; 33 5150 ed between the ground "or negative "terminal'flcif the' fil-te'r aim the point 41 which is-between' the resi'stanee '32 a'nd' mesecondar' or transformer I 31. A similar condenser 42 is connected between the ground and the conductor 29.

The filament supply circuit for tube T2 is shunted by a potentiometer resistance 45 which is engaged by a slider 46 grounded through the resistance 47. A relatively high capacity condenser 50 shunts the resistance 47. The grid'circuit of tube T2 is grounded and includes the secondary of an input transformer 51, the primary of which may be supplied with signal current from one or more preceding stages such as a detector stage or other amplifying stages.

7 With the connections 'arranged as shown in the positive terminal ofthe filter-' through the 7 primary 24 of theoutput transformer through the tube T1 to the filament supply circuit'of tube, through resistance 25, slider 26, conductor 29, primary 30 of transformerv 31., tube I12, filament supply circuit tor-tube T2, resistanceafi, slider 46, on resistance 47 togrpund; Inasmuehassliderfiii is grounded through resistance 27, alloithe plate current of tube T1 does not flow through the plate circuit :of tubeTZ'bu-t instead, a portionoiiit flows through the resistance 27 to ground; this resistance being of such value that the tube receives its proper plate wrrent and voltage, which as previously stated is less .than'the plate current and voltage of thejpower tube T1.

' The drop in voltage through that of the resistance 27 between the slider 26-and the slider 33 is .used to give the desired biasing potential-to the grid-oat tubeTl. A

It will be seen that the resistances}? and 132 are shunted by eondensersoland :42 whicheondensers form impedance; path-s tor the signal currents-inthe grid circuit of T1 and plate circuit of tube T2. These condensers serve toreduce the :coupling between'the grid and plate circuits of tube T1 and soprevent any substantial signal degenerative coupling effects which might occur the signal. current, .flowed through resistanee2'7. V

'Resistance 47 is employed t1 give. thedesired blam ng potential to the grid of tube T2. This resistance, it will be seen, is shunted by-the condenser 50, which serves as .a byepassfaround resistance 4'7 .f-or the low frequency S al currents for the grid circuit of T2.

The condenser 42m}! serve anxadditi'onalusd ful function in thesystem shown in Figure 1. This condenser; it will be seen, constitutes-3. coupling between the plate circuit of tube and the plate and. gridcircuits of tube Tl; This-cow pling if properly counectedzmay beemployed to produce regenerative effectsgwhich are inversely proportionalto the frequency of the'signa'lcurrents. As this coupling a capacity coupl'm-g, its efiectiveness' decreases .with" fr equencyiiand provides a-signazl voltage applied-to the plate circuit of tube T2 whose magnitude increases as the frequency is lowered. Thus the low frequency signal currents, which in systems now'in use are not amplified to as great a; degree as the higher frequencies, may in my'irnproved systembe amplified to an extent equal tothat of the higher frequencies. Itwill of course be understood that this coupling will not hemade .sufficiently great as .to cause the amplifier to oscillate atsome very low .frequency- If the coupling phase between the tubes Tland T2 be reversed by reversing either winding of the coupling transformer 31, the low frequency signal currents may, if desired, be reduced.

In Figure 1, I have shown two tubes with their plate circuits arranged in series relation. It will be understood that in addition to the tube T2 I may if desired employ other tubes, the plate circuit of each of which is in series withthe plate circuit of tube T1. The plate circuit of tube T2 and the plate circuits of each additional tube will in general be connected in parallel circuit relation to one another. Such additional tubes may for example be a first audio frequency amplifying tube and all "of the radio frequency amplifying tubes of the receiving system and in addition the detector tube whose plate may be connected to the point 54 at the positive side of the condenser 42 through a voltage reducing resistor.

In Figure 2 I show by Way of illustration an extension of the system of Figure 1 to include a first stage of audio frequency amplification preceded bya detector stage. In this Fig-ureT3 :represents an audio frequency amplifying tube injthe first stage of audio amplification and T4 represents a detector tube. .As will be seen the plates :of tubes T3 and T4 are. connected to the point fiiatthe positive side of the condenser 42, this. point being the positive potential'point for the =plate circuits of the tubes T2, T3 and T4. Plate-circuitsof tubes T2 and T3 are arranged in parallel with one another and the plate tube to provide the desired low plate voltage foroperation of this tube. V I i In Figure 2 I show the detector tube and first audio tube .of the directlyheated type, that is tubes having filament cathodes which are heated to operating temperature bycurrent therethrough. I may .however, if desired, employ a detector tube and first audio tube of the indirectly heated cathode type. When tubes of the-later type are used in the system shown in Figure 2;, the circuit arrangement shown in this figure provides-for preventing excessive voltage beingapplied to the condenser i2 during the initial period of slow heating of the tube cathodes and the same safeguard is had when these tubes are removed for any reason while the system is energized. This feature is mentioned because in the usual system where the potentials for the first audio tube, theradio' amplifier tubes and the detector tube are taken from the full potential of the filter through potential reducing resistances,

the removal of these tubes or their inactivity during the heating up period of the indirectly heated cathode type results in the high potential of the filter available for the power amplifier tube being appliedto the filter condensers of the plate supply circuits of the low potential tubes. Since for economical reasons it is desirable to use filter condensers designed to withstand the lower operating potentials-only, these transient high potentials endanger these condensers, and often damage them. In my present system the low potential tubes are permanently connected across their fractionalpart of the total filter potential, -so that removalof the tubes or inactivity of them cannotraise the potential to excessive values.

.In Figure 3' Ishow a. modified'circuit arrangement wherein part of the plate current of the power tube T1 serves as the plate current of the preceding amplifier tube'T2 and the remainder of the plate current. of tube T1 is employed for "dirtlygrounddor conncte iwjth the eg'ative terfisflonnected p'y'a wire as tu Ilir'rFigurefB, current frorn'fjthe' positive, terminal; 13+ of the filter passes tofthe'plate ortubeTlJ-thence to the am nt and mhs i rlzfi n.; aa e' Thernt th n. v des porti n m s n ithu ough conductor, 29 and primary of transformer ;3 1-,to. the-plate of tube 'I'Zand thencettothe fila- ,ment ofytube1-T2 and back tontheznegative termi- -;nal ofcithe filterify'lhe' remainder ofrthesplate current :Tofiq'tube Tl; flows fromsrthez sliderflfi throughfresi'stancel 27-, conductor 65', filament 1:0f tube 1T2; ,conductori 66',qba'ck1to;the negative iter- -minal-B:'aof ;the filter. wThe-platecurrent of tube T1 thus 1 serves as zithe plate current of :tube T2 ;and'-, also as the. filament :heatingficurrent of tube T2. r

?It;will be :seen that; in the .circuitiarrangernent of Figure *3, the :grid 50f? tube T19 is connected through the :secondaryoi transformer31 with the negative; terminal {of %the a filter and :that' the filamentr supply circuit of tube T1: is; connected to the. negative: terminal of the filter rthrough 7 two paths,;one {including the plate circuit ofttube T2 and the; other-pincludingqtheresistance 2'? 1 and the filament of 1 tube, g The resistance otthese two pathswis such as to givesthe required biasing voltage to; the grid oftuben'll. ':It will be understood that, in addition totubeTZ, I' may employ several; tubes deriving; gtheir L plate currents from ithe-source oisupplythroughithe plate circuit of the power tube T1 and with their several filaments arranged in serieswith one: anotherl'and in series with ,theiplateicircuit of tube T1;

-:While I have, indicated and described 'several' systemsiior; carryingimy invention: intoz efiect, it

vwill, be, apparent :jtooneskilled in :the art that my invention isgby' nomeans limited-to the particular .organiZationsZshown andidescrib'ed; butithat many modifications 1 may. :be :made without 3 departing irom-the scope of my inventionas set forth-in the appendedclaims- 1: Having: ithusdescribed my inventiomwwhat I claim 152 1 "331* .t? 51' L. :A' vm'ultiestagei:"amplifying :system comprising vacuum tubes having; coupled :plate and "grid circuits; means; including a source'of potential,

' providing a potential drop connected forenergizing the gridzof one'tube, and connectionstto said mean xr i i cluding the Liplate,v to cathode? path of said one tubeiorgutilizing,thesamesaid potential drop for energizing, the: 'platecircuit of.1:'another tubesaidwystem. "T 2. A multi-stageamplifying; system comprising va cuumtubeshaving plate {and grid circuits nontube with the difference,- or *potential {developedfor "one of said tubesand negatively to thin-filament pt: bems'cbiii e t thereof by wayof'a resistance, and connections or independently: energizing-the grid circuit of saic'ltube and the plate circuit of a preceding tube of the system-' with the diiferencc'e of p'otential developed by the current fio'w in said resistance. r

c 41 A m ulti stage amplifying system comprising vacuum tubes having; plate-and grid-circuits non-conductively connected in cascade, a source ofi'current connected positively to the plate jcir cuit of" one ot said tubes and negatively to the filament thereof by way I of a "resistance, and

connections f or independentlynegatively energiz -ing the gridof saidtubej andpositivel'y energiz' ing the plate or a preceding tube "of lthe system with thedifference of potential develcnpe by he currentflfiow insaid resistance; I

5.'-A multi'-'tage-'amplify"'g sy' tern, compris- -in'g vacuum tube s having' 'plateand grid circuits non-conductively connected in cascade, a source of current connected positively t the plate c rcuit-of one of 1 said tubes I and negativelyto the filament thereof by way of a resistance} connections for energizing "the grid cir'cuit of said tube eg e i nf fi nqte itia developed'by the current'flow inf's'aid jreslstaricy connections for positivelyenerg'izing'" the plate i w lu ali Pre edi tu iw thi t developeddifierence of potential, and meansfor cuit or circuits reducing the "potential supplied to the'p late cir v I "6. A m ulti-stage amplifyingfsystemfcompris 5 ing vacuum tubes havingl plate and grid "circuits i u t v nne ed i ws a' M ll of current connected positively to,j the plate" cirfcuit of'one of said tubes and negativelyi to he- 'fllamentthereo b Wa f a filament a vp ingitube and-laresistancemonnections qrneg tivel'y energizing the grid. circuit of saiqn mine with the ;difierejnce of potential. developed bycurrent flow in said (resistance, and connectionsior positively nergizing the platecircuit orfycircuits 'of one'or ore preceding tubes with said developeed diife'reneeofpotentialflii I. if 7. A .mu1ti-s"tage"signal currentfarnplifying system comprising vacuum tubes having plate and grid circuits 'non-conductively .connected in I cascade, a source of current, connected positively to the plate eircuit'ofv 'oneof fs aid tubesandfnegatively to the? filament thereotby way 0 1a re sistance, connections for independentlyrnegative- 1y energizinglthe I gri ijtr said tube and :posi- I iv ner i n a ep r d -t bl -i s st m; w t --d fi r of, e en a developedbythe current' flow in said resistance,

a d Qwj-- me ns-tor by-pa. sinss1 na1 qur aroun a re i ta q -w, 7

8. A multi-stage amplifyingsystem compris ing -'va cuum; 'tubesghaving; non-conductively coupled plate; and grid circuitay: a,- source, of

potential and 1 means including; a, ,com mon impedance, and-L-the plate-to cathode path o fjone ube o ner i in h ri c r u ts! a d o vacuum tubes having plateandgrld circuits nonf j conductively connected in ,1 cascade, "a source of current-connected positivelyqto the plate circuit of the last" tube and negatively :tof-the filament thereof :by'way of a; resistance, and; connections for independently energizing the grid icircuit'of saidslast tube andthej plate circuityofaprecedin'g tube ;with the: difierence of; potential ,dei

:velopedi by lt-he-icurrent; flow in said resistance, said last tube circuit-being connectedatora point pi said resistance of lower potential than the point of saidwresistance tojwhich :the said preceding plate circuit is connected. I 10. A multi-stage amplifying system comprisin va uum tubes having plate and grid circuits non-condueti-vely connected in cascade, a source 1 curre t, c c r i t lre therfleteicir? .cuit .of the last tube and negatively to the filae ,ment thereof by wayot a resistance, and connec- 1 9 1 53 dentl e izin h rid ircuitof said last-tube and the platev circuit, of a preceding tube 1 with the difference of potential develcped Jcy the current flow in-saidresistance, said last tube grid circuit ,being adjustably connccted to apoi-nt ,of, said resistance-of. lower poten ia tha t e, in s i r i t c to w i the-said preceding plate circuit is connected. ,1 l. ;A- multistage amplifying system comprising vacuuintubesfhaving;plate and grid circuits non-conductively connected in; cascade, a source of ,current connected positively to the plate circuit qflthe lasttube and negatively to the fila merit thereof. by vay of a resistance, and connectionsfor independently energizing the grid}.'cir cuit otsaid lasttubeand the plate circuit of a preceding" tube ,wi'thjthe difference of potential developed by the current flow in said resistance, vsaid;last tubegrid circuit and preceding tube plate circuit being connected to different points on said resistance.

1 2, 'A Qmulti-stage amplifying system. comprise ingvacuum tubes having plate and grid circuits non-,conductively connectedin cascade, a source offcurrent connected positively to the plate circuit. of the last tube and negatively to the ,'fi lament theregffby way of a resistance-and 'co'n'ne'c for indepei' deritly energizing the grid circuit ofsaid last tubeand theplate circuit of 'a'precedirig' tube with the difi erence of potential developed byjthe current flow in said resistance, said "precedingtube being disposed inadetector stage, and its said plate circuit, being connectedTto a point on said resistance of' higher potential than the point to which said last tube grid circuit is nhe d:

' i I 13.; ulti-stage amplifying system comprising vacuum tubes havin-g plate and grid circuits non-conductively connected in cascade, a source of current'connected positivelyto the plate circuit of the last tube and negatively to the I filamerit thereof by way of aresistance, and connections for independently energizing the {grid circuit-ofsaid las'ttubeand theplate circuit of'ja preceding tube with the difference of potential developed by the current flow in said resistance, and means for adjusting the energiza-tion of-said last tube grid circuit.

- 1'4."A mu1ti-stage amplifying system comprising vacuumtubes having plate and grid circuits 'non-conductiv'ely connected in cascade, a source -cf current connected positively to the plate circult of one of said tubes and negatively tothe filament thereof by way'of a resistance, and connections for independently energizing the grid circuit of'sa'id tube and the plate circuit of a preceding tube of thesystem withthe d'iiteren'ce of potential developed bythe current .flow "in said resistance, said resistance being ofsuch a magnitude-that said preceding plate circuit receives'less voltagethan the plate circuit of sai'dlfirst men :cui-tsnon-conductively ccnnectedin cascade, 1a source-,--o, current connected, positively tc plate-circuitrot one of said. tubes and negatively to the filament: thereof by way of a resistance, and connections-for independently energizing the grid circuit ,ofisaid tube and the plate circuit of a, preceding tube flf the system with the differ- "ence of potential developed by the current flow inr'saidresistance,'anda'dditional means for biasing the gridpfisa ild preceding tube.

16. A multi 'stage' amplifying system "comprisingvacuum tubes having plate and grid circuits non conductively connected in cascade, a source of current connected positively to the plate ctre'uit of'one of said tubes and negatively to the filament thereof by' way of a resistance, and connections for independently energizing the g'ridcircuitiof-said tube and the plate circuit of apreceding tube o'f the system-with the difference/of-potential developed by the current flow in saiduresistahcegar'id a low impedance capacitative path coupling said preceding plate circuit 'jand' the plate and grid circuits of said first mentioned tube.

- 17 A multistage amplify-ing system comprising vacuum tubes having plate and grid circuits non-conductively connected in cascade, a source ofrcur'rent connected positively to the plate circuitof one of said tubes and negatively to the filament thereof byway of a resistance, and connections'for independently energizing the grid circuit of: said .tubewand the plate circuit of a preceding tube of the 'system with the difference of: potential developed by the current flow in said resistance,a capacity connected to said preceding plate circuitand inishunt with said-re- 'sistanc'e, and asecond'capacity connected to the grid circuit of said-first' 'tub'eancl in shunt with said'resistance. i V

i 18. A multi-stage amplifying system comprising vacuum tubes having plate and'grid circuits non condu'cti-vely connected "in cascade, a source :ofcurrent connected positively to the plate circuitpfs the last wbeiandnegativelyto the filanections for independently energizing the grid circuit of said 'last'tube and; the plate circuit of a preceding tubewith the difference of potennections for independently energizing the grid 1 circuit of saidlasttube and the plate circuit of a preceding tube with theediflference of potential developed by the current flow in said resistance, a detector tube-coupled to said preceding tube,

and means for connecting the detector plate circu'itto said resistance. r

1 2}). A multi-sta'ge amplifying system comprisiing vacuum tubes having plate and grid circuits 'nonconductively connected in cascade, a sourceof currentnconne'ctedpositively to the plate circuituofthe last'tubeiand negatively to the filamentithereof by way of-a resistance, and connections for independently energizing the grid circuit of said last tube and the plate circuit of 5 ing tubes having plate and grid cinla-r preceding tube with the difference of potential vinent thereof by way 101" a resistance, and cong second connection resistor.

o 1,985,945 developed by the current flow in said resistance,

a source of current for energizing the electrodes of said tubes, the anode of the audio tube being connected to a point of positive potential of said source, a second connection between the cathode of the audio tube and a point of negative potential of the said source, said last connection including a control grid bias resistor, a third connection from the control grid of the audio tube to a point on said bias resistor, a connection for applying a desired positive potential to the anode of said detector tube, and an audio frequency feed-back condenser, of low impedance to audio frequency currents, connected between the anode of said detector tube and a point on said adjacent one side of the bias 22. In combination with a receiver network including a detector tube and audio amplifier tube coupled in cascade, a source of energizing potential for the said tubes, connections for applying positive potentials, derived from said source, to the anodes of said tubes, an impedance in the space current circuit of the audio tube, and a condenser connected from a point in the said space current circuit between the audio tube cathode and said impedance and the anode circuit of the detector tube for feeding back alternating current potentials developed across said impedance. I I

23. In combination with a receiver network including a detector tube and audio amplifier tube coupled in cascade, a source of energizing potential for the said tubes, connections for applying positive potentials, derived from said source, to the anodes of said tubes, an impedance in the space current circuit of the audio tube, a connection between the control grid of the audio tubeand said impedance, and a condenser connected from a point in the said space current circuitbetween the audio tube cathode and said impedance and the anode circuit of the detector tube for feeding back alternating current potentials developed across said impedance.

24. In combination with a receiver networkincluding a detector tube and audio amplifier tube coupled in cascade, a source of energizing potential for the said tubes, connections for applying 'to which the second connection is made. V r

26. In a receiver-network, at least two from positive potentials, derived from said source, to the anodes of said tubes, an impedance in the space current circuit of the audio tube, thecatH- odes'of said detector and audio tubes being at relativelyinvariant direct current potentials,

a condenser connected from a point in the said space current circuit between the audio tube cathode and said impedance and the anode'circuit of the detector tube for feeding back alternating current potentials developed across said impedance; 7 l a 25. In a receiver network, at, least two nonconductively cascaded tubes, a source of energizing potential for the electrodes of the tubes, eachtube being provided with a cathode and a plurality of cold electrodes, a biasing resistorin the space current circuit of the second of said tubes,

a connectionfrom the positive side of said sourcev to a cold electrode of the second tube, a second connection from another cold electrode of the second tube to saidbias resistor, and a third" connection from a cold electrode of the first of said tubes to a point of said bias resistor which is at a'positive potential with respect to the'poin conductively cascaded tubes, a source of e'nergizing potential for the electrodes of the tubes,

each tube being provided with a cathode and a' plurality of cold electrodes, a biasing res'istor'in the space current circuit of the second of said tubes, a connection from the positive side of said source to a cold electrode of the second tubepa second connection from another cold electrode of the second tube to said bias resistor, and a, third connection from a cold electrode of the'first of saidtubes to a point of said bias resistor which is at a positive potential with respect to the point to which the second connection is made, a biasing resistor in the cathode circuit of the first tube,

and a fourth connection between anothericold electrode of the first tube and the last bias resistor.

named 27. A multi-stage system comprising electron discharge tubes having output and input circuits of current connected positively to the plate cirof the last tube. by way of a resistance, and connections for independently energizing the control grid circuit of the last tube and a positive cuit of the last tube and negatively to the cathode cold electrode circuit of a preceding tube with the difference of potential developed by the current fiow in said resistance, BENJAMIN F. MIESSNER.

45 non-conductively connected in cascade, a source 

